The Virtex-5 FPGA family has rules about power-up ramp times outlined in
Table 6 on Page 6 of the DC & Switching specifications:
http://www.xilinx.com/support/documentation/data_sheets/ds202.pdf
On the face of it, the Virtex-5 spec claims that these special power-up
ramp times apply to ALL power forms (VCCint, VCCaux, VCCo). However, we
suspect that they're really intended for VCCint & VCCaux, and probably
irrelevent for VCCo (Xilinx is just covering their arse by making a
blanket application to all VCC's?).
Since we're finding it difficult to create room on the PWB for all of
the special "soft start" Linear* Regulators to handle all of the power
supplies for our Virtex-5, we were wondering if anyone else can confirm
or deny the efficacy in taking shortcuts with the VCC__ ramp times
(VCCint & VCCaux = ramp-rate important; VCCo = not so much). i.e., Did
your volume/production (not onesies-twosies) Virtex-5 design work while
violating power-up ramp times for one or more VCC's?
Your thoughts & experiences are appreciated.
* (our application can not tolerate Switching Regulators)